Koga Irrigation Scheme is one of the potential watermelon producing areas in Ethiopia. However, the average yield of watermelon is low due to inappropriate sowing date and poor agronomic practice like vine pruning. Therefore, a field experiment was carried out during 2021/22 irrigation season to evaluate the influences of sowing date and number of vine on growth, yield and quality of watermelon at Koga irrigation scheme, North Mecha woreda, West Gojjam Zone, Ethiopia. The experiment consisted of three sowing dates (D1: November 12, D2: December 12 and D3: January 12) and four number of vines (VP1: without pruning, VP2: 2 vine, VP3: 3 vine, and VP4: 4 vine arranged with factorial combination in Random Complete Block Design with three replications. Data’s on phenology, growth, yield and physico-chemical quality attributes were collected and analysed by using Statistical Analysis Software (SAS) version 9.4. The results clearly showed that, data’s on days to 50% flowering, maturity, number of lateral branch per vine, leaf area, vine length, fruit size classification, fruit per vine and per plant, marketable, unmarketable and total fruit yields, and total soluble solids were influenced by date of sowing and number of vines. The interaction effect of sowing date and number of vine influences on number of lateral branch per vine, number of fruit per plant, unmarketable yield and, fruit size category. Moreover, significantly maximum marketable tuber yields of watermelon were obtained from seeds sown at January date and maintained three number of vines per plant with the values of (45.7 t ha-1) and (42.15 t ha-1) respectively. Based on the partial budget analysis, watermelon sown during January combined with three vines gave the highest net benefit (1,121,616.00 Birr ha-1) and marginal rate of returns (1,944%). Based on the results of the present study, sowing of watermelon in the month January and maintaining three vines per plants recorded the highest marketable yield and better fruit quality of watermelon, which can be recommended for economical production of the crop in the study area and areas with similar agro ecologies.